Alkenes

• What is the general formula for alkenes?

  C$n$H$2n$
• Why are alkenes classified as unsaturated?

  Because they have two fewer hydrogen atoms than the corresponding alkane
• What is the molecular formula of ethene?


  C$2$H$4$
• What does the displayed formula of a molecule show?

  It shows all of the atoms and the covalent bonds
• If an alkene has three carbon atoms, what is its molecular formula?

  C$3$H$6$
• How do you calculate the number of hydrogen atoms in an alkene?

  Multiply the number of carbon atoms by two
• What is the molecular formula of butene?


  C$4$H$8$
• In which position can the double bond be placed in butene for GCSE level?

  Between any two adjacent carbon atoms
• What is the molecular formula of pentene?

  C$5$H$10$
• How many hydrogen atoms does ethane have?

  Six hydrogen atoms
• How many fewer hydrogen atoms do alkenes have compared to alkanes with the same number of carbon atoms?

  Two fewer hydrogen atoms
• What is the displayed formula of ethene?

  It shows the arrangement of two carbon atoms with a double bond and four hydrogen atoms
• What are the key alkenes you should learn for your exam?

  • Ethene (C$2$H$4$)
  • Propene (C$3$H$6$)
  • Butene (C$4$H$8$)
  • Pentene (C$5$H$10$)
• What are the characteristics of alkenes?

  • Contain at least one double bond
  • General formula: C$n$H$2n$
  • Unsaturated due to fewer hydrogen atoms compared to alkanes
• How do you derive the molecular formula of an alkene from the number of carbon atoms?

  1. Identify the number of carbon atoms (n).
  2. Use the formula C$n$H$2n$ to find the number of hydrogen atoms.